So now America’s biggest business lobby and late-night comic David Letterman have something in common: They have really, really embarrassed themselves.

Of course, there are significant differences between Letterman’s womanizing and the U.S. Chamber of Commerce’s backward-looking opposition to climate-change legislation, which is causing the chamber to lose members, prestige and, worst of all, clout.

For one thing, the chamber’s blunder was entirely unnecessary.

For another, the chamber has yet to apologize.

But the bottom line is that the chamber is embarrassed, or should be. It has lost a number of high profile members -- utility companies Exelon, PG&E and PNM Resources and, most recently, Apple, whose image as a forward-looking company left the chamber looking stuck in the past. (One clever headline put it, Apple, citing climate, tells U.S. Chamber iQuit) A Nike executive resigned from the chamber board. Tuesday’s New York Times and Washington Post featured full-page ads from big companies and environmentalists calling upon the U.S. Senate to “pass clean energy legislation with a cap on greenhouse gas emissions this year.” The ads were signed by, among others, Dow, Exelon, United Technologies, Duke Energy, GE, Weyerhauser, Constellation Energy, Interface, PSEG, Deutsche Bank, Entergy, Johnson Controls and NRG. That was a direct slap at the chamber, too.

{related_content}Chamber CEO Tom Donahue can’t say he wasn’t warned.

Consider the fact that more than two-and-a-half years ago -- on January 22, 2007, to be precise -- the CEOS of some of the chamber’s most important, high-profile members -- GE’s Jeff Immelt, DuPont’s Chad Holliday, Duke Energy’s Jim Rogers, among them -- stood besides some of America’s most important environmentalists, including Fred Krupp of the Environmental Defense Fund and Jonathan Lash of the World Resources Institute, to declare that anthropogenic global warming is a problem and

"to call on the federal government to enact legislation requiring significant reductions of greenhouse gas emissions."

True, there weren’t a lot of policy details when the U.S. Climate Action Partnership was launched but the message was clear: Big Business, or at least a significant number of big businesses, wanted mandatory U.S. government regulation to curb global warming. Since then, U.S. CAP, as it’s known, has attracted new members, including AES, Chrysler, ConocoPhillips, Deere & Company, Dow Chemical, Exelon, Ford, General Motors, Johnson & Johnson, NRG Energy, PepsiCo, Rio Tinto, Shell, and Siemens. Not a list you’d want to ignore.

But the chamber, for reasons that remain unclear, continued to oppose -- and not just oppose, propagandize against -- any climate legislation with a real chance of passage.

In other words, the association did what no smart association should do: It ignored some of its most powerful members. Starting last year, the problem became glaringly evident. Environmentalists (led by Pete Altman of NRDC) and reporters were putting the spotlight on the gap between the chamber’s position and the position of some of its most visible members. I wrote a column called Climate Change Schizophrenia that ran on Slate’s The Big Money back in April and asked, Why do corporations support regulating greenhouse gases but fund a lobby that opposes it? Sources tell me that a delegation from companies that belong to U.S. CAP went to see Donahue the chamber’s CEO to talk about climate policy, and they got the brushoff.

To be sure, the chamber, which calls itself “the voice of business” and spent about $62 million lobbying Congress last year, also has lots of members from the oil, coal and energy-intensive industries who oppose federal regulation of greenhouse gases. Its 122-member board includes executives from Consol Energy, Massey Energy, Peabody Energy and the Southern Co.

The smart thing for the chamber to do would be to stay neutral -- to admit that business is divided on the issue and to leave lobbying up to individual companies. Instead, some chamber officials offered up reasonable arguments against the bills pending in Congress and others went off the deep end. In a remark that was ill-advised at best and downright dumb at worst, William Kovacs, the chamber’s senior vice president for environment, technology and regulatory affairs, called for a public trial about climate science that he said would be “the Scopes monkey trial of the 21st century.”

That wasn’t an isolated remark. In comments filed with the EPA when the agency said it would regulate carbon emissions, the chamber argued that maybe global warming wasn’t so bad after all. As Kate Sheppard reported for Mother Jones, the chamber submitted a document called “Detailed Review of EPA’s Health and Welfare Scientific Evidence,” that says:

"Humans have become less susceptible to the effects of heat due to a combination of adaptations, particularly air conditioning. The availability of air conditioning is expected to continue to increase."

And:

"Overall, there is strong evidence that populations can acclimatize to warmer climates via a range of behavioral, physiological, and technological adaptations."

And finally:

"[T]he scientific evidence is clear that cold is a more potent hazard than heat."

This is a little nutty, and it’s hard to know why the chamber would venture so far outside of the mainstream. Maybe ideological blinders? It’s long been more friendly to Republicans and opposed to government regulation. Maybe conflicts of interest. In a provocative blogpost, Pete Altman argued that Donahue, who sits on the board of the Union Pacific Railroad, has a personal interest in the issue–he’s been paid more than $1.1 million by the railroad, and given another $3.8 milion in stock -- because the railroad is a major shipper of coal.

In the end, it doesn’t matter much. What matters is that the chamber can’t any longer pretend to be the voice of  business on the climate change issue -- the biggest business controversy of the decade. Now that’s embarassing.

GreenBiz.com Senior Writer Marc Gunther maintains a blog at MarcGunther.com.

Historic U.S. Chamber of Commerce Building -- Photo by Ian Wagreich via U.S. Chamber of Commerce